1) Is there minimum length of pipe from the boiler where the primary loop ends? I mean, can I place the closely spaced tees sic inches from the boiler, or is it better to make a larger loop so there is more flow and water running thru the primary loop?

2) The boiler has 1" fittings and my piping is 3/4". Where is the best place to step down to 3/4"? Would it be OK to go directly from the 1" stubs on the boiler to 3/4" with a step 1" to 3/4" fitting or should I run 1" pipe for a while or maybe to the closely spaced tees?

You should read the installation instructions. You absolutely cannot reduce the primary inlet/outlet or the primary piping to 3/4" It appears that you do not have an understanding of hydronic theory. It would be a shame to spend all that money and time and then have to tear it all out and do it all over again. You should find a competent technician and have the job done right.

Thanks Tom. I do understand that the primary loop must be 1". I asked the question before finishing the directions and from looking at the way the oil boiler was installed (with 1-1/4" boiler in/outs to eventually 3/4") I was just thinking of an easier way of doing it with all the 3/4" supplies I have. I do understand hydraulics and thermodynamics and have taken classes in these subjects too. My main question is in reference to question #1 which the directions does not address. Do you know if there is an optimum length for the primary loop with the closely spaced tees. I can place the tees 12 inches from the boiler, or would, say, 4 feet be better. Would the four feet create too much heat loss and the opposite hold true for the 12" length.

Thanks Tom. I do understand that the primary loop must be 1". I asked the question before finishing the directions and from looking at the way the oil boiler was installed (with 1-1/4" boiler in/outs to eventually 3/4") I was just thinking of an easier way of doing it with all the 3/4" supplies I have. I do understand hydraulics and thermodynamics and have taken classes in these subjects too. My main question is in reference to question #1 which the directions does not address. Do you know if there is an optimum length for the primary loop with the closely spaced tees. I can place the tees 12 inches from the boiler, or would, say, 4 feet be better. Would the four feet create too much heat loss and the opposite hold true for the 12" length.

Tom - You're a Sweetheart. I came on this forum to get help. It's a DIY forum. Even your title is "DIY Senior Member" I don't know why you can't answer a simple question with a simple answer rather than trying to berate me. I'm a licensed PE in 3 states and do all my home improvement work myself. I took on this project since it's the summer and I have 5 months to get it done. I know how to solder, wire and do simple projects like this. I took these classes I mentioned over 10 years ago and I'm sure you don't remember every tidbit of information you have learned. I asked 3 simple questions on this forum and you have done nothing but comment rudely for a DIY forum where people come for answers. My neighbor is an HVAC Contractor and he is going to sign off on my project. I'm trying not to bother him with questions like these, but I guess I'm going to have to since this forum sucks with not answering simple questions. Go Love yourself and your family.

Ah, so since its a DIY forum that means you are entitled to free advice even when it's obvious that you don't have the requisite knowledge to even contemplate installing condensing gas equipment so I should as you put it DIE. Well, just because I feel that it's important to keep the ignorant from doing just that and perhaps killing their family and loved ones as well I shall now give you the best advice you are likely to get here or anywhere else for that matter. Call a licensed gas appliance installer.

I guess you didn't read the part "My neighbor is an HVAC Contractor and he is going to sign off on my project". He is a licensed installer. He knows my talent and skills and is very confident that I can do the job. If I make a mistake, he will not let me fire it up until it's 100% correct. He is going to check everything BEFORE any water is filled in the system or the gas is turned on. Being he is so kind, I'm trying to not bother him so much with the simple questions that I thought would be kindly answered. Some of them have been by others in this forum, but not by you. And yes, these forums are normally for free advise, but I guess you are just a plumber who thinks he is above everyone one else.

I would never fire it up without having a licensed installer (my Neighbor) look it over and sign off on it. I'm not that crazy and I don't want any problems or accidents. I'm just trying to save money by doing something I am fully capable to do. It's not rocket science.

Very True and that's why I'm asking questions, making calls to technical support, following the piping diagram in the manual, and all of the manuals recommendations and warnings and having a licensed installer double check me. Once I finish, I'll post photo's to prove my pure talent of great workmanship.

I would never fire it up without having a licensed installer (my Neighbor) look it over and sign off on it. I'm not that crazy and I don't want any problems or accidents. I'm just trying to save money by doing something I am fully capable to do. It's not rocket science.

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Sign off what? Did you pull a permit? Have you notified the gas company? You do know that the gas company needs to inspect the gas piping yes?

That you are having to ask questions that are so very basic in nature tells us that you are not fully capable of doing the work. If you were "fully" capable you would already know about primary/secondary piping and you would already know the best practice for venting the unit. Knowing how to solder does not fully capable make. Do you understand that installing a condensing boiler on a system that most likely is fed by copper fin tube baseboard will almost certainly mean that your boiler will never condense and therefore never come close to the efficiencies you think it will. In fact, if the unit doesn't condense your efficiencies will be in the mid 80's But you probably didn't take that into account did you? And if you didn't not only will the unit not run at maximum efficiency, it will also short cycle which will reduce the life of the burner and components and cause you to make a bunch of phone calls to Triangle Tube. There's a reason why we have a license and well,,,,,,as far as I know rocket scientists don't

I ask because the min-fire output on that sucker could handle the heat load on my ~2400' not-so-insulated house at Long Island's ~ +15F 99% outside design temp, and would be ridiculously oversized (and short-cycling) on my smaller zones. The -60 is a better match for the loads for the vast majority of existing homes on L.I., and at high fire it could heat my house at 90-100F below zero (!), temps not seen on Long Island since the last ice age.

Oversizing a mod-con boiler is a common mistake (even from licensed HVAC installers) and leads to paying too much up front, lower average efficiency, and short-cycling the thing to higher maintenance &/or an early grave. Before you get too far along the installation, let's first make sure it's even the right size boiler.

Now, before you've turned on the power or fired up the burner is the right (and cheapest) time to make any corrections, and I'm telling you straight out, the -110 is too big for almost any average sized house in your area, even oversized for some bigger houses, and if you have it broken up into zones it can be a real PITA to hack the system into working properly with an oversized boiler.

All good heating system designs start with a careful room-by-room heat load calculation, but unless you're planning on tweaking the radiation, let's simplify it by doing the whole-house load numbers, and the zone-by-zone radiation numbers to see if the -110 would run reasonably, or if you need to down size.

Start with the approximate size (square footage of conditoined area) of the house, exterior wall area & nsulation type/mounts, attic area and window type/amount, window type & total area, door area, and total square footage of the house.

Foundation insulation (Y/N)?

Then how many zones, and how much radiation (and type) per zone?

If you have a heating fuel use history on the place from a prior boiler, pick a mid-winter bill, note the meter-reading dates, and give us your zip code (for degree-day weather history), and the amount of fuel used in that time period. Then give us the BTU-in and DOE BTU out of the prior boiler. This kind of calculation can be more precise than doing it by the building parameters, or would at least put a realistic hard upper bound on what your whole house heat load is.

From the pictures on another thread I suspect he is past the point of return. Again and again they come to these sites asking questions when it's already too late to do anything about it. You are correct in surmising that the 110 is too big. I suspect its almost twice as much as needed and I also suspect that the system is 3/4" high temp copper fin tube baseboard that is looking for boiler temps near 200 degrees. So, as I said in the last post, the unit will short cycle and never come close to condensing return temperatures. Essentially, he has spent a whole lot of money and gained nothing but remember, according to him he is more than capable of installing the unit. Primary loop piping won't make a bit of difference and in fact, since the whole system is not matched, primary/secondary is a waste of time and materials. Might as well pipe it straight out and back. A 200 gallon buffer tank might help though but then, you're heating 200 gallons of water for what? Oh yea, to pick up 8 to 10% efficiency....or do the numbers start to run backwards from ther lol scratching head.

At 200F it doesn't take much fin-tube to cover the +15F heat load of a typical 2500' rancher on Long Island- even 50' would do it for most. Hopefully he has a heluva lot more fin-tube than that, or he's screwed with the -110.

Being capable of doing the plumbing isn't the same as being able to assess the system design. I s'pose that what the neighbor-buddy was going to be doing for him(?), but if that's the case, I'd hazard he didn't even do the crayon-on-napkin math, unless this is a 4500' uninsulated barn with single-pane glass (with some panes broken), in which case the money would have been far better spent tightening up the place.

[edited to add]

philtrap: Before finishing off the plumbing take the time to figure out the answers to the questions on my prior post. Any fixes in the design should rightly be done BEFORE you throw the switch, whether you keep the Solo-110 or not, rather than having to hack into the system when it starts misbehaving. You'll probably want it fully vetted, tested, & tweaked before the heating season begins. If you are going to need to buffer it to kill off the short cycling, making the buffer tank your hydraulic separator may be better than whatever primary/secondary scheme you're currently working on.

At min-mod on the Solo-110 and an 8F of hyseresis (I'd have to look up whether that's even programmable with the Solo series) you can get better than 3 minutes min-burn out of a 25-30 gallon high-mass hydraulic separator which would at least save the boiler from early death. It won't modulate the way you'd LIKE to be able to do with a mod-con when appropriately sized, but it won't burn out by doing 100,000 ignition cycles a season. If you're radiation-limited or have only fin-tube for heat emitters you would always be putting out at least 120F water into the radiation independent of load, and there are versions of massive hydraulic separator/buffers out there with internal heat exchangers for potable domestic hot water. (eg, ErgoMax E23). There's some crayon-math required to determine whether that's an appropriate solution here though- need to know the real heat load, and the real heat emitters, etc. and there'd be some tweaking of the outdoor reset curve limits and the aquastat on the tank to keep it all within the delta-T limits of the boiler a any season, yet still give good hot water performance, during the summer, etc.

But I'm getting ahead of myself here- let's pencil out the true heat load and radiation conditions first, and figure out if it's too late to pack the boiler back up once we determine in black & white what we're all feeling gut-wise, that a smaller boiler would be more appropriate for your actual loads & radiation.